140 MRS. ERNEST HART, 
be 1 per cent., it is only necessary to add 9000, but if 
the strength of the solution be less it is necessary to multiply 
the number of corpuscles by the figure representing the 
dilution before adding 0000. To correctly estimate 
the number of white corpuscles per cubic millimeter a 
much larger area must be taken, and for this purpose the 
rectangles of 5 square mm. have been drawn on the slide. 
The number of white corpuscles found in ten of these large 
rectangles must be counted. If in a 1 per cent. solution the 
number of white corpuscles in ten of these large rectangles 
is found to be thirty, then we know, as above shown, that 
the volume of the solution counted is— 
10 x 3, x torl0 x z45 = Hy mm? 
The number counted, therefore, multiplied by 10 and then 
by 100, will give at once the number of white corpuscles in 
a cubic mm. of blood; or, in other words, it is only neces- 
sary, for a one per cent. solution, to count and add 000. 
For example: 
30 x 10 x 100 = 30,000. 
This method of estimating the number of white corpucles 
will be felt by every worker at this subject to be a great 
gain, for on this point none of the previous instruments 
gave any but the roughest approximate results, likely to 
give rise to the most delusive conclusions. ‘To sum up, the 
advantages of this new Compte-Globules over that first intro- 
duced by M. Malassez are that it can be used clinically 
with any microscope, that no particular skill is required to 
use it, and only ordinary care to keep it clean and in order. 
Over other clinical Corpuscle-Counters it possesses the 
merits—of making the layer of fluid accurately + mm. in 
depth, so that there are no corrections to make; of having 
the squares ruled to the smallest size yet found possible, so 
that the numeration is exceedingly easy and not fatiguing 
to the eyesight; of making an exact computation of the 
number of white corpuscles per cubic mm.; and, lastly, by 
means of the rack movement of the carrier of the cover- 
glass, and by the use of the Melangeur Potain, of preserving 
the homogeneity of the drop when placed on the slide and 
flattened to the depth of + mm. 
The counting of blood-corpuscles is now so common and 
frequent an operation in clinical medicine, and its value in 
assisting diagnosis and treatment is so well recognised, that 
I feel sure that insistence on the minute details and scrupu- 
